doubt on FET characteristics

[sita]

hi.

I have a doubt on what's the reason for a small slope in saturation region of drain current v/s. drain-source voltage after the MOSFET attains pinch-off.

If you have any good books describing this interesting MOSFET internal actions, please do share.

Thanks,
sita

 

[avi_e-]

Hi Friend,

There are many books for this. Refer
* Electronic Devices and Circuit Theory - Nashelsky and Boylestad
* Electronic Devices and Circuits - David A. Bell
* Electronic Devices - Salivahanan
* Electronic Devices - Macmillan & Halkias


Regards,
Avinash.S.

 

[A.Anand Srinivasan]

in the equation for current you can see Length(L) in the denominator.... when pinch off is reached the length slowly starts decreasing which compensates for the increase in Vgs and hence a slow slope is obtained...

 

[LvW]

hi.

I have a doubt on what's the reason for a small slope in saturation region of drain current v/s. drain-source voltage after the MOSFET attains pinch-off.

Do you mean MOSFET operation below threshold ? This is typical for log domain applications (logarithmic law instead of quadratic behaviour).

 

[octocreation]

Hi,

At saturation, FET will have nearly constant and maximum current and current merely increases with VDS. But with the influence of Channel Length modulation λ, there is influence of r0≈(1/λIsat) which will lead to a slope.

regds,
anup

 

[LvW]

Hi,
..... But with the influence of Channel Length modulation λ, there is influence of r0≈(1/λIsat) which will lead to a slope.

This effect is quite similar to the EARLY effect for BJT´s.

 

[venkat_kode]

this is called Channel-Length Modulation

chk this explanation